1. Field of the Invention
This application claims the benefit of priority to Japanese Patent Application No. 2004-181551 filed on Jun. 18, 2004, herein incorporated by reference.
The present invention relates to a rotating member-supporting structure and a rotation detecting device having the same, or more specifically, to a means for suppressing the eccentricity of the rotating member with respect to a guide unit.
2. Description of the Related Art
Conventionally, as a rotation detecting device which is applied to a rudder angle sensor for a car or the like, a device is known, which includes a case-shaped attaching member on which a through-hole for a rotating member is provided, a rotating member which is held through the through-hole, a code plate which is attached to the rotating member and rotatably housed in the attaching member, and signal detecting elements which are provided inside the attaching member and operate in conjunction with the code plate to detect signals in accordance with the rotating state of the rotating member (for example, see Japanese Unexamined Patent Application Publication No. 2000-241144).
In this type of rotation detecting device, since the through-hole which is provided on the attaching member functions as a guide unit of the rotating member, the clearance between the guide unit and the rotating member needs to be as small as possible in order to suppress the eccentricity of the rotating member and to obtain high resolution of signal detection.
Meanwhile, the attaching member and the rotating member are made of an unreinforced plastic material such as polyolefin methacrylate, acrylic resin, or polybutylene terephthalate in the related art because of the excellent abrasion resistance.
The rudder angle sensor for a car must be sustainable for operation in the temperature range of −40° C. to +85° C. Therefore, it must be expected that there will be clearance in the range of 0.3 mm to 0.5 mm, since thermal expansion of the attaching member and the rotating member and thermal distortion of the attaching member cause positional deviation between the guide units provided at the upper and lower surfaces of the attaching member when the above-mentioned plastic material is used.
However, in recent years, since high resolution of one degree or more is required in this type of the rotation detecting device, if the clearance between the guide unit and the rotating member is allowed in the range of 0.3 mm to 0.5 mm, the eccentricity of the rotating member becomes large, and it is impossible to realize required resolution.